Question

我有许多具有可变长度行的csv文件。例如以下内容：

Time,0,8,18,46,132,163,224,238,267,303
X,0,14,14,14,15,16,17,15,15,15
Time,0,4,13,22,32,41,50,59,69,78,87,97,106,115,125,127,137,146,155,165,174,183,192,202,211,220,230,239,248,258,267,277,289,298,308
Y,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
Time,0,4,13,22,32,41,50,59,69,78,87,97,106,115,125,127,137,146,155,165,174,183,192,202,211,220,230,239,248,258,267,277,289,298,308
Z,0,1,2,1,1,1,1,1,1,2,2,1,0,1,1,2,2,2,2,2,1,1,2,2,2,1,1,1,1,1,2,2,2,2,2
Time,0,308
W,0,0

变为：

Time,X,Time,Y,Time,Z,Time,W
0,0,0,0,0,0,0,0
8,14,4,0,4,1,308,0

许多数据已经丢失，只占用了前两个数据。

我想在python中转置这个CSV。我有以下程序：

import csv
import os
from itertools import izip
import sys

try:
    filename = sys.argv[1]
except IndexError:
    print 'Please add a filename'
    exit(-1)
with open(os.path.splitext(filename)[0] + '_t.csv', 'wb') as outfile, open(filename, 'rb') as infile:
    a = izip(*csv.reader(infile))
    csv.writer(outfile).writerows(a)

然而，它似乎削减了大量数据，因为文件从20KB下降到6KB并且只保持最小行长度。

如何不丢弃任何数据？

Answer 1

izip根据最短的数组进行拉链，因此您只获得每行中最短数组长度的值。

你应该使用izip_longest而不是那个，它用最长的数组拉链，并且在没有值的地方放置None。

示例 -

import csv
import os
from itertools import izip_longest
import sys

try:
    filename = sys.argv[1]
except IndexError:
    print 'Please add a filename'
    exit(-1)
with open(os.path.splitext(filename)[0] + '_t.csv', 'wb') as outfile, open(filename, 'rb') as infile:
    a = izip_longest(*csv.reader(infile))
    csv.writer(outfile).writerows(a)

我从中获得了结果 -

Time,X,Time,Y,Time,Z,Time,W

0,0,0,0,0,0,0,0

8,14,4,0,4,1,308,0

18,14,13,1,13,2,,

46,14,22,1,22,1,,

132,15,32,1,32,1,,

163,16,41,1,41,1,,

224,17,50,1,50,1,,

238,15,59,1,59,1,,

267,15,69,1,69,1,,

303,15,78,1,78,2,,

,,87,1,87,2,,

,,97,1,97,1,,

,,106,1,106,0,,

,,115,1,115,1,,

,,125,1,125,1,,

,,127,1,127,2,,

,,137,1,137,2,,

,,146,1,146,2,,

,,155,1,155,2,,

,,165,1,165,2,,

,,174,1,174,1,,

,,183,1,183,1,,

,,192,1,192,2,,

,,202,1,202,2,,

,,211,1,211,2,,

,,220,1,220,1,,

,,230,1,230,1,,

,,239,1,239,1,,

,,248,1,248,1,,

,,258,1,258,1,,

,,267,1,267,2,,

,,277,1,277,2,,

,,289,1,289,2,,

,,298,1,298,2,,

,,308,1,308,2,,

Answer 2

这是一种没有itertools.izip的方法：

import csv

with open('transpose.csv') as infile, \
        open('out.csv', 'w') as outfile:
    reader = csv.reader(infile)
    writer = csv.writer(outfile)
    while True:
        try:
            index = next(reader)
            data = next(reader)
        except StopIteration:
            break
        writer.writerows(zip(index, data))

根据您的输入，此代码段会生成以下out.csv：

Time,X
568,0
573,0
577,1
581,1
585,0
590,2
594,0
599,0
603,0
Time,Y
590,0
594,3
599,3
03,0
Time,Z
599,0
603,1

这是你想要的吗？

更新

此修改后的示例应与您更新的问题相符：

import csv
from itertools import zip_longest  # izip_longest in Python 2

with open('transpose.csv') as infile, \
        open('out.csv', 'w') as outfile:
    reader = csv.reader(infile)
    writer = csv.writer(outfile)

    writer.writerows(zip_longest(*reader, fillvalue=0))

将fillvalue更新为您要用。替换缺失值的内容。

在python中以不同的行长转置csv

2 个答案:

更新